New Trends in Nanotechnology and Fractional Calculus ...download.e-bookshelf.de/download/0000/0728/79/L-G-0000072879... · Çankaya University, Balgat-Ankara, Turkey ... scientists

New Trends in Nanotechnologyand Fractional Calculus Applications

New Trends inNanotechnology andFractional CalculusApplications

Edited by

D. BALEANUÇankaya University,Balgat-Ankara, Turkey

Z.B. GÜVENÇÇankaya University,Balgat-Ankara, Turkey

and

J.A. TENREIRO MACHADOInstitute of Engineering of Porto,Porto, Portugal

123

EditorsDumitru BaleanuÇankaya UniversityFac. Art and SciencesOgretmenler Cad. 1406530 AnkaraYüzüncü Yil, [email protected]

Ziya B. GüvençÇankaya UniversityFac. Engineering & ArchitectureOgretmenler Cad. 1406530 AnkaraYüzüncü Yil, [email protected]

J.A. Tenreiro MachadoInstitute of Engineeringof the Polytechnic Institute of PortoDept. Electrotechnical EngineeringRua Dr. Antonio Bernardino de Almeida4200-072 [email protected]

ISBN 978-90-481-3292-8 e-ISBN 978-90-481-3293-5DOI 10.1007/978-90-481-3293-5Springer Dordrecht Heidelberg London New York

Library of Congress Control Number: 2009942132

c©Springer Science+Business Media B.V. 2010No part of this work may be reproduced, stored in a retrieval system, or transmitted in any form or byany means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without writtenpermission from the Publisher, with the exception of any material supplied specifically for the purposeof being entered and executed on a computer system, for exclusive use by the purchaser of the work.

Cover design: eStudio Calamar S.L.

Printed on acid-free paper

Springer is part of Springer Science+Business Media (www.springer.com)

Preface

By the beginning of November 2008, the International Workshops on New Trendsin Science and Technology (NTST 08) and Fractional Differentiation and itsApplications (FDA08) were held at Cankaya University, Ankara, Turkey. Theseevents provided a place to exchange recent developments and progresses in severalemerging scientific areas, namely nanoscience, nonlinear science and complex-ity, symmetries and integrability, and application of fractional calculus in science,engineering, economics and finance.

The organizing committees have invited presentations from experts represent-ing the international community of scholars and welcomed contributions from thegrowing number of researchers who are applying these tools to solve complex tech-nical problems. Unlike the more established techniques of physics and engineering,the new methods are still under development and modern work is proceeding byboth expanding the capabilities of these approaches and by widening their range ofapplications. Hence, the interested reader will find papers here that focus on the un-derlying mathematics and physics that extend the ideas into new domains, and thatapply well established methods to experimental and to theoretical problems.

This book contains some of the contributions that were presented at NTST08and FDA08 and, after being carefully selected and peer-reviewed, were expandedand grouped into five main sections entitled “New Trends in Nanotechnology”,“Techniques and Applications”, “Mathematical Tools”, “Fractional Modelling” and“Fractional Control Systems”.

The selection of improved papers for publication in this book reflects the successof the workshops, with the emergence of a variety of novel areas of applications.Bearing these ideas in mind the guest editors would like to honor many distinguishedscientists that have promoted the development of nanoscience and fractional calcu-lus and, in particular, Prof. George M. Zaslavsky that supported early this specialissue and passed away recently.

The organizing committees wish to express their thanks to Cem Ozdogan, AdnanBilgen, Ozlem Defterli, Burcin Tuna, Nazmi Battal as well as to our students fortheir assistance.

The Editors would like to thank to Ozlem Defterli for helping in preparation ofthis book.

v

vi Preface

The organizing committees wish to thank the sponsors and supporters of NTST08and FDA08, namely Cankaya University represented by the President of the Boardof Trustees Sıtkı Alp, the Rector Professor Ziya B. Guvenc, TUBITAK (The Scien-tific and Technological Research Council of Turkey), and the IFAC, for providingthe resources needed to hold this conference, the invited speakers for sharing theirexpertise and knowledge, and the participants for their enthusiastic contributions tothe discussions and debates.

Ankara Dumitru BaleanuMarch 31, 2009 Ziya B. Guvenc

J.A. Tenreiro Machado

Contents

Part I New Trends in Nanotechnology

Novel Molecular Diodes Developed by Chemical Conjugationof Carbon Nanotubes with Peptide Nucleic Acid : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 3Krishna V. Singh, Miroslav Penchev, Xiaoye Jing,Alfredo A. Martinez–Morales, Cengiz S. Ozkan, andMihri Ozkan

Hybrid Single Walled Carbon Nanotube FETs for HighFidelity DNA Detection : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 17Xu Wang, Mihri Ozkan, Gurer Budak, Ziya B. Guvenc,and Cengiz S. Ozkan

Towards Integrated Nanoelectronic and Photonic Devices: : : : : : : : : : : : : : : : : : : 25Alexander Quandt, Maurizio Ferrari, and Giancarlo C. Righini

New Noninvasive Methods for ‘Reading’ of Random Sequencesand Their Applications in Nanotechnology : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 43Raoul R. Nigmatullin

Quantum Confinement in Nanometric Structures : : : : : : : : : : : : : : : : : : : : : : : : : : : : 57Magdalena L. Ciurea and Vladimir Iancu

Part II Techniques and Applications

Air-Fuel Ratio Control of an Internal Combustion EngineUsing CRONE Control Extended to LPV Systems : : : : : : : : : : : : : : : : : : : : : : : : : : : 71Mathieu Moze, Jocelyn Sabatier, and Alain Oustaloup

Non Integer Order Operators Implementation via SwitchedCapacitors Technology : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 87Riccardo Caponetto, Giovanni Dongola, Luigi Fortuna,and Antonio Gallo

vii

viii Contents

Analysis of the Fractional Dynamics of an Ultracapacitorand Its Application to a Buck-Boost Converter :: : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 97A. Parreno, P. Roncero-Sanchez, X. del Toro Garcıa, V. Feliu,and F. Castillo

Approximation of a Fractance by a Network of Four IdenticalRC Cells Arranged in Gamma and a Purely Capacitive Cell : : : : : : : : : : : : : : : :107Xavier Moreau, Firas Khemane, Rachid Malti, and Pascal Serrier

Part III Mathematical Tools

On Deterministic Fractional Models : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :123Margarita Rivero, Juan J. Trujillo, and M. Pilar Velasco

A New Approach for Stability Analysis of Linear Discrete-TimeFractional-Order Systems : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :151Said Guermah, Said Djennoune, and Maamar Bettayeb

Stability of Fractional-Delay Systems: A Practical Approach : : : : : : : : : : : : : : :163Farshad Merrikh-Bayat

Comparing Numerical Methods for Solving NonlinearFractional Order Differential Equations : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :171Farhad Farokhi, Mohammad Haeri, and Mohammad SalehTavazoei

Fractional-Order Backward-Difference Definition FormulaAnalysis : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :181Piotr Ostalczyk

Fractional Differential Equations on Algebroids and FractionalAlgebroids : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :193Oana Chis, Ioan Despi, and Dumitru Opris

Generalized Hankel Transform and Fractional Integralson the Spaces of Generalized Functions : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :203Kuldeep Singh Gehlot and Dinesh N. Vyas

Some Bounds on Maximum Number of Frequencies Existingin Oscillations Produced by Linear Fractional Order Systems : : : : : : : : : : : : : :213Sadegh Bolouki, Mohammad Haeri, Mohammad Saleh Tavazoei,and Milad Siami

Fractional Derivatives with Fuzzy Exponent : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :221Witold Kosinski

Game Problems for Fractional-Order Systems : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :233Arkadii Chikrii and Ivan Matychyn

Contents ix

Synchronization Analysis of Two Networks: : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :243Changpin Li and Weigang Sun

Part IV Fractional Modelling

Modeling Ultracapacitors as Fractional-Order Systems : : : : : : : : : : : : : : : : : : : : :257Yang Wang, Tom T. Hartley, Carl F. Lorenzo, Jay L. Adams,Joan E. Carletta, and Robert J. Veillette

IPMC Actuators Non Integer Order Models : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :263Riccardo Caponetto, Giovanni Dongola, Luigi Fortuna,Antonio Gallo, and Salvatore Graziani

On the Implementation of a Limited Frequency BandIntegrator and Application to Energetic Material IgnitionPrediction : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :273Jocelyn Sabatier, Mathieu Merveillaut, Alain Oustaloup,Cyril Gruau, and Herve Trumel

Fractional Order Model of Beam Heating Processand Its Experimental Verification : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :287Andrzej Dzielinski and Dominik Sierociuk

Analytical Design Method for Fractional Order ControllerUsing Fractional Reference Model : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :295Badreddine Boudjehem, Djalil Boudjehem, and Hicham Tebbikh

On Observability of Nonlinear Discrete-Time Fractional-OrderControl Systems : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :305Dorota Mozyrska and Zbigniew Bartosiewicz

Chaotic Fractional Order Delayed Cellular Neural Network : : : : : : : : : : : : : : : :313Vedat Celik and Yakup Demir

Fractional Wavelet Transform for the Quantitative SpectralAnalysis of Two-Component System : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :321Murat Kanbur, Ibrahim Narin, Esra Ozdemir, Erdal Dinc,and Dumitru Baleanu

Fractional Wavelet Transform and Chemometric Calibrationsfor the Simultaneous Determination of Amlodipineand Valsartan in Their Complex Mixture : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :333Mustafa Celebier, Sacide Altınoz, and Erdal Dinc

x Contents

Part V Fractional Control Systems

Analytical Impulse Response of Third Generation CRONEControl : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :343Rim Jallouli-Khlif, Pierre Melchior, F. Levron, Nabil Derbel,and Alain Oustaloup

Stability Analysis of Fractional Order Universal AdaptiveStabilization : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :357Yan Li and YangQuan Chen

Position and Velocity Control of a Servo by Using GPCof Arbitrary Real Order : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :369Miguel Romero Hortelano, Ines Tejado Balsera, Blas ManuelVinagre Jara, and Angel Perez de Madrid y Pablo

Decentralized CRONE Control of mxn Multivariable Systemwith Time-Delay : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :377Dominique Nelson-Gruel, Patrick Lanusse, and Alain Oustaloup

Fractional Order Adaptive Control for Cogging EffectCompensation : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :393Ying Luo, YangQuan Chen, and Hyo-Sung Ahn

Generalized Predictive Control of Arbitrary Real Order : : : : : : : : : : : : : : : : : : : :411Miguel Romero Hortelano, Angel Perez de Madrid y Pablo,Carolina Manoso Hierro, and Roberto Hernandez Berlinches

Frequency Response Based CACSD for Fractional OrderSystems : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :419Robin De Keyser, Clara Ionescu, and Corneliu Lazar

Resonance and Stability Conditions for Fractional TransferFunctions of the Second Kind : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :429Rachid Malti, Xavier Moreau, and Firas Khemane

Synchronization of Fractional-Order Chaotic Systemvia Adaptive PID Controller :: : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :445Mohammad Mahmoudian, Reza Ghaderi, Abolfazl Ranjbar,Jalil Sadati, Seyed Hassan Hosseinnia, and Shaher Momani

On Fractional Control Strategy for Four-Wheel-SteeringVehicle : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :453Ning Chen, Nan Chen, and Ye Chen

Fractional Order Sliding Mode Controller Designfor Fractional Order Dynamic Systems : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :463Mehmet Onder Efe

Contents xi

A Fractional Order Adaptation Law for Integer Order SlidingMode Control of a 2DOF Robot : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :471Mehmet Onder Efe

Synchronization of Chaotic Nonlinear Gyros Using FractionalOrder Controller : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :479Hadi Delavari, Reza Ghaderi, Abolfazl Ranjbar,and Shaher Momani

Nyquist Envelope of Fractional Order Transfer Functionswith Parametric Uncertainty : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :487Nusret Tan, M. Mine Ozyetkin, and Celaleddin Yeroglu

Synchronization of Gyro Systems via Fractional-OrderAdaptive Controller : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :495Seyed Hassan Hosseinnia, Reza Ghaderi, Abolfazl Ranjbar,Jalil Sadati, and Shaher Momani

Controllability and Minimum Energy Control Problemof Fractional Discrete-Time Systems : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :503Jerzy Klamka

Control of Chaos via Fractional-Order State FeedbackController :: : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :511Seyed Hassan Hosseinnia, Reza Ghaderi, Abolfazl Ranjbar,Farzad Abdous, and Shaher Momani

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .521

Part INew Trends in Nanotechnology

Novel Molecular Diodes Developed by ChemicalConjugation of Carbon Nanotubes with PeptideNucleic Acid

Krishna V. Singh, Miroslav Penchev, Xiaoye Jing,Alfredo A. Martinez–Morales, Cengiz S. Ozkan, and Mihri Ozkan

Abstract In this work single walled carbon nanotube (SWNT)-peptide nucleic acid(PNA) conjugates are synthesized and their electrical properties are characterized.Metal contacts to SWNT-PNA-SWNT conjugates, used for current–voltage (I–V )measurements, are fabricated by two different methods: direct placement on pre-patterned gold electrodes and metal deposition using focused ion beam (FIB). Back-gated I–V measurements are used to determine the electronic properties of theseconjugates. Additionally, conductive atomic force microscopy (C-AFM) is used tocharacterize the intrinsic charge transport characteristics of individual PNA clusters.

As electronic devices scale down, traditional lithography-based fabrication meth-ods face unprecedented challenges more than ever before [1,2]. The need for novelbottom up techniques to get over the hurdle posed by downscaling is getting in-creasingly urgent [3–5]. Molecular electronics, based on the unique self-assemblycapabilities of molecules, exemplifies the idea of bottom-up fabrication approach[6, 7]. Therefore, the study of the electrical properties of single molecular com-ponents, can serve as a starting point for the study and realization of molecularelectronics. Carbon nanotubes (CNTs) based bioconjugates are a suitable candidatefor molecular electronics as they incorporate the excellent electrical and structuralproperties of CNTs [8,9] and the self assembly properties of bio-molecules [10–12].In our previous work, we have synthesized single walled carbon nanotube (SWNT)-peptide nucleic acid (PNA) conjugates [13]. The main aim behind this work is totest these conjugates for their future use in molecular electronics applications.

The as-synthesized conjugates have the following structure: two SWNT ropesjoined by a PNA cluster, where PNA acts as a linker to bring two SWNT ropes

K.V. SinghDepartment of Chemical and Environmental Engineering, University of California,Riverside, CA 92521

M. Penchev, X. Jing, A.A. Martinez–Morales, and M. Ozkan (�)Department of Electrical Engineering, University of California, Riverside, CA 92521e-mail: [email protected]; [email protected]

C.S. OzkanDepartment of Mechanical Engineering, University of California, Riverside, CA 92521

D. Baleanu et al. (eds.), New Trends in Nanotechnology and FractionalCalculus Applications, DOI 10.1007/978-90-481-3293-5 1,c� Springer Science+Business Media B.V. 2010

3

[email protected]

[email protected]

4 K.V. Singh et al.

together. Due to their unique structure these conjugates can serve a twofoldedpurpose. On one hand, they can be used to develop CNT based molecular devicesas SWNTs are functionalized and conjugated with a molecule. On the other hand,CNTs can act as electrodes to electrically characterize and test the functionality ofPNA. In fact, till date there is no report on electrical transport through PNA. Usingthis approach of conjugating SWNTs with PNA, provides us with a tool to test forsuch electrical characteristics. Hence this work also reports the use of single-walledcarbon nanotubes (SWNTs) as a wiring alternative for molecular-scale devices. Theappropriate nanometer dimensions, chemical and mechanical stability, and high car-rier mobility make SWNTs an ideal candidate for the same [14]. Due to theseadvantages provided by SWNTs as components for molecular devices, lots of ad-vances have been made to incorporate them into molecular device platform [15–17].These include the development of high quality nanotube syntheses and integratedmolecular-SWNT chemical and biological sensors [18]. The biggest challenge inusing SWNTs as wires for molecular circuits is to engineer synthesis techniquesof combining molecules with SWNTs in a way that it will not affect the intrinsicelectrical transport properties of SWNTs. This work also overcome this challengeby optimizing the functionalization of SWNTs which result in predominant end ox-idation and hence incorporation of PNA molecules at the tip of tubes [13].

The major challenge in electrically characterizing these conjugates was fab-ricating electrodes/contacts to measure their electrical transport. Two differenttechniques: direct placement on pre-patterned gold electrodes and focused ion beam(FIB) were utilized according to the available resources and technology to developthese contacts. In addition, individual PNA clusters were also characterized by con-ductive atomic force microscopy (C-AFM). The electrical transport results presentvery interesting phenomena for these conjugates. The conjugates have asymmet-rical electrical transport, allowing current to flow only in one direction, at roomtemperature which corresponds to diodic or rectifying behavior. In addition someconjugates also show characteristics of negative differential resistance (NDR) [19].In this work, back-gated measurements on conjugates were also performed, allow-ing us to determine the transconductance and mobility of the conjugates. Therefore,this work presents electrical properties of novel SWNT-PNA-SWNT conjugates andin addition also comments on the conductivity of PNA.

The synthesis route for producing these conjugates is given in detail in our pre-vious report [13]. Differently to our previous work, here we have used highly pureHiPCO SWNTs [20] to increase the reliability of electrical transport results as theSWNTs conduct through their surface [21]. Due to decrease in the impurities inSWNT structure, which contribute towards faster oxidation of SWNTs, we have tomodify oxidation conditions. The new optimized oxidation conditions for predom-inantly end functionalization (as required) [13] of SWNTs are 14 h of acid refluxin 2.4 M of HNO3. Increase in oxidation time and also the strength of acid usedin this work (previously 12 h and 1 M HNO3/ is a strong indicative of the purity ofSWNTs employed in the synthesis of these SWNT-PNA conjugates. After oxidationand subsequent sonication of SWNTs, SWNT bearing NHS esters were prepared bycoupling with EDC and NHS [13]. Both end functionalization of PNA (AcLys–GTGCTCATGGTG-Lys-NH2) led to formation of SWNT-PNA-SWNT conjugates

Novel Molecular Diodes Developed by Chemical Conjugation of Carbon Nanotubes 5

Fig. 1 SEM micrograph of a SWNT-PNA-SWNT conjugate

as an amide bond is formed between the amine of the amino-acid residue on thePNA backbone and SWNT-bearing NHS esters [13]. A typical scanning electronmicroscopy (SEM) image of a SWNT-PNA-SWNT conjugate is shown in Fig. 1.In this work we also modified the amino acid residue on the PNA backbone toLysine to improve the solubility of PNA in water.

After synthesis of the SWNT-PNA-SWNT conjugates, electrical contacts werefabricated at the ends of individual conjugates by the following methods. The firstmethod consists of a direct placement on pre-patterned gold electrodes. One blockof four gold electrodes was patterned on Si=SiO2 chips. The structure of one elec-trode consist of a large square pad (L � 125�m) which is connected to a long metalstrip approximately 80�m long. In one block there were four such electrodes andin the center of the block the separation between the metal strips is around 1�m.On one single chip there were 289 such blocks. In the direct placement method theconjugates are deposited by drop casting; bridging across the metal strips due to thelength of SWNTs. After locating the connected strips on a particular block, the elec-trical measurements are done by connecting the bigger pads of the correspondingmetal strips to external probes (tip diameter � 1�m) in a probe station (Signatone).Using an Agilent 4155 C semiconductor parameter analyzer the I–V characteristicsof these conjugates were obtained.

The major advantage of this method is the simplicity and less time consumptionin preparing the sample for electrical characterization. But the major drawback isthat this method works on “hit and trial” basis and locating a single conjugate con-nected across two metal strips is a time consuming step. In addition, the contactbetween the conjugate and the electrode is not necessarily good (as the conjugateis sitting on top of the electrode) and can create artifacts during the measurements.Sometimes it is also possible that whole chip does not have the required connectionor electrodes are not connected by the right conjugates.

The second method used for fabricating the contacts employs the use of focusedion beam (FIB). It consists of an electron beam (SEM) as well as an ion beam(Gallium ions). This technique provides us the opportunity to visualize the con-jugates (by SEM) and develop the contacts directly on the conjugates by metaldeposition assisted by the ion beam (Leo XB1540). The required conjugate is

6 K.V. Singh et al.

located on the pre-patterned electrode system (as discussed above) by SEM. Themeasurements are made at the same time for the contacts. Then the deposition ofmetal (i.e. Platinum) takes place by the following procedure. A gas containing metalions is introduced into the system and allowed to chemisorb onto the sample. Byscanning an area with the ion beam, the precursor gas is decomposed into volatileand non-volatile components; the non-volatile component (platinum metal) remainson the surface as a deposition while the volatile component is vaporized. One majoradvantage of this system is that one can monitor the formation of contacts in realtime under SEM.

This technique overcomes the disadvantages of less control, lack of precisionand “hit and trial” approach of the previous technique discussed above. But thistechnique has its own set of issues, which mainly include the destruction of sampleby ion beam and shifting (if the system is not calibrated precisely). In order toavoid damaging the SWNT-PNA conjugates, the following parameters were chosen:deposition current of 2�A and scanning frequency of 0.1 Hz, which worked well forour conjugates. In addition, this technique can also be used to repair the damagedelectrodes after measurements and the same conjugate can be reused, which is notpossible by the other technique. Moreover, destructive ion milling can also be usedas means to isolate the conjugate from other materials. For this purpose currentshigher than 50�A were used.

In order to report the first electrical conductivity measurements of PNAmolecules, we prepared samples for C-AFM analysis (Fig. 3) by drop casting asolution of PNA (100�M concentration) on an oxygen plasma cleaned n-type Sisubstrate. Oxygen plasma cleaning ensured the removal of any carbonaceous impu-rities as they might interfere with the final results since PNA is also carbonaceousin nature. During CAFM measurements a Pt/Ir coated AFM tip (�20 nm radiusof curvature) was used as a top contact to measure the current with respect to anapplied bias voltage. The electrical measurements were taken by first performinga morphology scan in contact mode and then driving the tip by a point and shootmethod to the top of a specific PNA cluster.

After contact fabrication the SWNT-PNA-SWNT conjugates were tested by dif-ferent methods as described above. Most of the conjugates show asymmetricalcurrent–voltage (I–V ) characteristic. Most of which show a rectifying or diodic be-havior. This behavior was independent of the method used to fabricate the contacts.Typical diodic behavior is shown in Fig. 2a, c. In addition some conjugates alsoshow negative differential resistance, which is characteristic of resonance tunnelingdiode (RTD). Figure 2b, d represent the NDR characteristic of few conjugates. Con-trol devices based on SWNT-only samples were also fabricated and the results areshown in Fig. 2e, f.

Additionally, the intrinsic charge transport characteristics of individual PNAclusters (Fig. 3 inset) were also studied by C-AFM measurements. As shown inFig. 3, typical PNA current–voltage measurements at the nanoscale exhibit a rectify-ing behavior analogous to the I–V curves observed for the SWNT-PNA conjugates.For the negative tip bias voltages, a steep and exponential increase of the tun-neling current occurs beyond a threshold voltage of �6V. The turn-on voltage


Fig. 2 Two terminal electrical characterization of SWNT-PNA-SWNT conjugates. (a) and (c)Diodic behavior is observed for both direct placement and focused ion beam (FIB) method. (b)and (d) Similarly, negative differential resistance behavior was observed in few conjugates forboth methods. (e) and (f) SWNTs-only samples show symmetric behavior with high conductivityirrespective of method

observed in the PNA cluster is in good agreement with the measurements madeon the SWNT-PNA conjugates (Fig. 2a). It is also interesting to point out that PNAshows extremely good current-blocking behavior under positive tip bias voltage ofup to 10 V.

8 K.V. Singh et al.

Fig. 3 Charge transport characterization by C-AFM. The I–V curve shows a characteristic diodicbehavior for a single PNA cluster. Inset: AFM topography image of a single PNA cluster

Field effect transistors (FETs) were fabricated on single conjugates by usinga Si=SiO2 substrate as the back-gate, as the back gate and insulator respectively,during the electrical measurements. A representative I–V curve for these gatedstudies is represented in Fig. 4a showing that the SWNT-PNA-based FETs behaveas ‘p’ type conjugates. Few conjugates did not show any change in conductivityon applying a gate voltage (Fig. 4b). To further test the electrical properties ofour device structure control devices based on SWNT ropes alone (Fig. 4c, d) werealso fabricated. The ropes which were semiconducting were found to be ‘p’ typewhile metallic ropes do not show any semiconducting behavior. The back-gatedmeasurements were used to determine transconductance and mobility of the SWNT-PNA-SWNT conjugate FET device (Fig. 4e, f).

The diodic behavior observed in the SWNT-PNA-SWNT conjugates is not anew phenomenon in molecular electronics. In 1974 Aviram and Ratner proposeda molecule based rectifying behavior [22]. That work was one of the pioneers in thefield of molecular electronics. Since then there have been numerous efforts to de-velop AR theory based rectifiers. In the literature, there are several molecules whichhave shown this rectifying behavior [23–25] but this kind of observation is madehere for the first time for PNA. The mechanism for this rectifying behavior is ex-plained in detail elsewhere [23–25]. In short, for an ideal AR molecular diode, therectifying molecule has a D-¢-A structure, where D is a good electron donor, ¢ isthe insulating bridge and A is the good electron acceptor. The rectifying behavior ofthe molecule is observed when this molecule is connected to the conductors (Con-ductor (C1)-Molecule (M)-Conductor (C2)) on both ends. The mechanism involvestwo molecular orbitals, the highest occupied molecular orbital (HOMO), mainlylocalized on D, which would be filled, and the lowest unoccupied molecular or-bital (LUMO), mainly localized on A. Electrons transfer from one contact to theother contact by tunneling through the D-¢-A molecule which forms the preferen-tially excited electronic state. DC-¢-A�. Inelastic “downhill” tunneling within themolecule (involving either phonon emission or photon emission) then would reset


Fig. 4 FET characterization. (a) and (b) Gated study of SWNT-PNA-SWNT conjugates. Theelectrical behavior of the conjugates is modulated by the type of SWNTs connecting the conju-gate. (c) and (d) SWNT ropes are shown to behave either as ‘p’ type semiconductors or metallic,respectively. (e) Transconductance of SWNT-PNA-SWNT conjugates. (f) Mobility of SWNT-PNA-SWNT conjugates

10 K.V. Singh et al.

the ground state D-¢-A, but an electron would have been moved from metal elec-trode C1 to metal C2; hence the rectifying effect [11]. The proposed molecule wasnever synthesized, but helped in developing the theory behind the rectifying behav-ior of molecules in molecular electronics. The observance of diodic behavior is alsodue to the chemical structure of the molecule. When the relevant molecular energy isin resonance with the Fermi level of the metal electrode, there is a dramatic increasein the current through the molecule, and a dramatic selectivity of electron transportthrough the C1-M-C2 sandwich [26]. Hence when the molecular orbitals of PNAcome to resonance with the molecular orbitals of SWNTs attached to them, there isan observed increase in the current. But this phenomenon is not reversible and thecurrent can only be conducted in one direction only. Therefore, both the structureand contact of PNA with conductors (i.e. SWNTs) on both ends are responsible forthe diodic behavior observed in the conjugates (Fig. 2a, c). Furthermore, the obser-vance of diodic behavior of the PNA clusters in conductive AFM (Fig. 3) is also dueto this C1-M-C2 sandwich. In this case the conductors are the AFM tip (metal) onthe top and Silicon (semiconductor) on the bottom. This observation further sup-ports the fact that the observed diodic behavior of SWNT-PNA-SWNT conjugatesis not because of SWNTs contact with PNA but rather due to the PNA itself.

The exact mechanism of transfer between SWNT-PNA-SWNT will require ex-tensive modeling based on molecular dynamics. Only then we can locate the variousmolecular orbitals in the conjugates and their behavior under an external electricfield. But the mechanism explained above gives us a right start in this direction.

As far as NDR effect is concerned, there are many reports on observation ofNDR in molecular electronics [27, 28]. Many mechanisms have been proposed forthe same but there is no consensus in the literature. In fact, we have previously ob-served a similar NDR behavior in our earlier work related to SWNT-DNA-SWNTconjugates [29]. Since the bonding between SWNT and DNA is analogous to theone between SWNT and PNA, we propose the following qualitative explanationfor the observance of NDR effect in SWNT-PNA-SWNT conjugates (Fig. 5) [29].At zero bias voltage, chains of SWNT-PNA-SWNT conjugates have uniform Fermi

Fig. 5 Schematic illustration of electrons transferring through energy barriers of PNA molecules


energy levels. When applied voltage increases, energy levels tilt and electrons starttunneling from the voltage source through the energy barriers of PNA molecules.Correspondently, current increases until the localized energy band inside quantumwell shifts to below Fermi energy from the voltage source, leaving no correspond-ing energy levels for after-tunneling electrons to stay. As a result, current starts todecrease. As the applied voltage continues to increase, the higher unoccupied en-ergy levels in PNA shift down to the energy level which are in alignment with theFermi energy from the energy source and current starts to increase again. Since ourconjugates consists of SWNT ropes formed by many intertwined tubes and in con-sequence of numerous PNA molecules, alignment and misalignment do not happenat the same voltage, it is reasonable that we get multiple current peaks for differentSWNT-PNA conjugates.

In addition, Lake et al. [30] have postulated SWNT-pseudo peptide-SWNTnanostructure could exhibit RTD I–V response via computations based on the den-sity functional theory (DFT) and non-equilibrium Green function (NEGF) approach.Our results are in accordance with these theoretical and experimental analyses.

Control measurements were done on SWNT ropes alone with a two-fold purpose.Firstly, to differentiate the electrical characteristics obtained for the conjugates ver-sus the electrical properties of SWNT ropes. Secondly, to indirectly prove that PNAis indeed joining two different SWNT ropes. Representative I–V curves of SWNTropes (Fig. 2e, f) show a symmetrical nature and higher conductivity for the ropes.The electrical characteristics clearly show that the ropes are fundamentally a differ-ent system from that of the conjugates.

The gated study presented in this work is the first of its kind for PNA basedcarbon nanotube conjugates. It was found that the conjugates were semiconduct-ing as well as metallic (Fig. 4a, b). A control study was also performed on SWNTropes alone (Fig. 4c, d). Few of the ropes were found to be metallic and some tobe semiconducting, as expected. But the difference in the nature of SWNT-PNA-SWNT conjugates can also be explained on the basis of SWNTs. Since PNA is verysmall compared to SWNTs and also much less conductive than SWNTs (as shownin I–V characteristics); the influence on total gated behavior will be modulated bythe SWNTs of the conjugate. If PNA is attached to semiconducting SWNTs on boththe ends, the conjugate will behave as semiconductor but if either or both of theSWNTs are metallic the conjugate will then behave as a metallic component.

Overall, the gated study confirms that PNA behaves as a hole conductingmolecule. This study also confirms the theoretical model explained elsewherefor CNT-Peptide-CNT system [31]. Lake et al. modeled the peptide molecule andfound out that peptide linker acts as a good bridge for hole transmission in the CNTvalence band and strongly suppresses electron transmission in the CNT conductionband [31].

During the electrical characterization of these conjugates, the biggest challengewas to understand the difference in behavior observed among different conjugates.The reason for this variation could be result of the following three main factors:variation in number of SWNTs, variation of number of PNAs, and variation of thetype of SWNTs in the conjugates.


The SWNTs used here are ropes and these ropes attach themselves to PNAmolecules by covalent coupling as described above. But all the ropes are not ofsame diameter and hence do not contain the same number of tubes. Therefore, thisvariation in number of tubes will always be observed from one conjugate to another.This variation in number of tubes on both sides of a PNA cluster will also changethe number of PNAs from one conjugate to another. But the number of PNAs canbe estimated by the following methodology.

The number of PNA attached in one conjugate can be calculated from the di-ameter of the SWNT rope in that sample. Haddon et al. reported that the efficiencyof the oxidation process for carbon nanotubes (tubes @ Rice are approximated forHiPCO tubes) is around 2% [32]. In this work we have preferentially oxidized thetips of SWNTs. Therefore, we can estimate the number of oxidized carbon atoms atthe tip by this formula:

; D Number of oxidized carbon atoms in on tube

D�

� � dtube

Length of C–C bond in SWNT .nm/

�� .Efficiency of oxidation process/

where, dtube W Diameter of single tube (nm)It is estimated that on an average in a SWNT rope of 20 nm diameter there are

around 500 tubes [33]. To get the number of oxidized sites in a rope (�), we canmultiply ; with rope correction factor ‰ (which gives the number of SWNTs in onerope of diameter davg.)

where ' D�davg

20.nm/

�� 500

Therefore,

˝ D Number of oxidized carbon atoms in one rope D ; � '

The efficiency of esterification (formation of SWNT-NHS esters) is nearly 100%as the intermediates are in excess. As per the chemistry, we also keep the amines(in our case PNA) in excess. Therefore, all the oxidation sites on the SWNT ropeswill be utilized by PNA molecules. Since for one site we can only have one PNAmolecule attached the number of PNA molecules attached will be equal to �.

A major challenge of using SWNTs in bulk or in solution is that it contains bothmetallic and semiconducting tubes/ropes. There is no easy way to separate them andutilize them separately. Our conjugates also suffer from this inherent disadvantage.In the conjugates, three types of configuration are possible; metallic (M)-PNA-M,semiconducting (SC)-PNA-SC and SC-PNA-M; will occur. In fact, this variationis clearly verified by the gated study of these conjugates. This configuration willaffect the shape, position of NDR peaks and nature of the current–voltage responsefor SWNT-PNA-SWNT conjugates since the resonance of energy levels betweenSWNTs and PNA is responsible for the rectifying nature of these conjugates.


As discussed above, in addition to developing SWNT based devices, thisstructure could also served as a way of utilizing SWNTs as electrodes for thecharacterization of molecular structures. The most common method of testingmolecules electrically is by Langmuir-Blodgett (LB) thin films [26, 34, 35]. Incontrast to the LB thin film technique there are several advantages in using thearchitecture presented in this work for characterization of molecules. First, theelectrical transport is confined to one dimension along the molecules, whereas inthe thin film approach, conduction also takes place along the latitudinal directionas well. Second, the number of molecules attached is restricted by the couplingsites available on the SWNTs, permitting high accuracy in calculating the num-ber of molecules attached. The number of functionalized sites in a rope/tube canbe estimated (as explained above). Therefore, from the number of these sites thenumber of attached molecules can also be calculated. Third, CNTs themselves haveexceptional electronic properties and also have excellent mechanical and chemi-cal properties as well that could be useful for the characterization of the intrinsicproperties of molecules.

In summary, we have synthesized single walled carbon nanotube (SWNT)-peptide nucleic acid (PNA) conjugates, which are characterized by severaldifferent techniques to determine their electrical properties. Our results demon-strate that the conjugates exhibit rectifying and negative differential resistance I–Vcharacteristics, making them ideal candidates for future electronic applications [36]as molecular diodes. Furthermore, the excellent structural and electrical propertiesof SWNTs enable us to use them as test electrodes in order to study the electricaland electronic properties of PNA cluster.

Acknowledgements We gratefully acknowledge financial support from the NanomanufacturingProgram of the National Science Foundation (NSF) (grant no: 0800680), the FCRP Center onFunctional Engineered Nano Architectonics funded by the SRC and DARPA, and the Center forHierarchical Manufacturing (CHM) funded by the NSF.

References

1. Lin BJ (2006) The ending of optical lithography and the prospects of its successors. Micro-electronic Engineering 83(4–9):604–613

2. Lin BJ (2006) Optical lithography—present and future challenges. Comptes Rendus Physique7(8):858–874

3. Huang Y, Duan XF, Cui Y, Lauhon LJ, Kim KH, Lieber CM (2001) Logic gates and computa-tion from assembled nanowire building blocks. Science 294(5545): 1313–1317

4. Cui Y, Lieber CM (2001) Functional nanoscale electronic devices assembled using siliconnanowire building blocks. Science 291(5505):851–853

5. Lu W, Lieber CM (2007) Nanoelectronics from the bottom up. Nature Materials 6(11):841–8506. Fu L, Cao L, Liu Y, Zhu D (2004) Molecular and nanoscale materials and devices in electronics.

Advances in Colloid and Interface Science 111(3):133–1577. Balzani V, Credi A, Venturi, M (2003) Molecular logic circuits. Chemphyschem 4(1):49–598. Baughman RH, Zakhidov AA, de Heer WA (2002) Carbon nanotubes – the route toward

applications. Science 297(5582):787–792


9. Wildoer JWG, Venema LC, Rinzler AG, Smalley RE, Dekker C (1998) Electronic structure ofatomically resolved carbon nanotubes. Nature 391(6662): 59–62

10. Bashir R (2001) DNA-mediated artificial nanobiostructures: state of the art and future direc-tions. Superlattices and Microstructures 29(1):1–16

11. Chakrabarti R, Klibanov AM (2003) Nanocrystals modified with peptide nucleic acids (PNAs)for selective self-assembly and DNA detection. Journal of the American Chemical Society125(41):12531–12540

12. Vernille JP, Kovell LC, Schneider JW (2004) Peptide nucleic acid (PNA) amphiphiles: Synthe-sis, self-assembly, and duplex stability. Bioconjugate Chemistry 15(6):1314–1321

13. Singh KV, Pandey RR, Wang X Lake R, Ozkan CS, Wang K, Ozkan M (2006) Covalent func-tionalization of single walled carbon nanotubes with peptide nucleic acid: Nanocomponentsfor molecular level electronics. Carbon 44(9):1730–1739

14. Star A, Han TR, Gabriel JCP, Bradley K, Gruner G (2003) Interaction of aromatic compoundswith carbon nanotubes: Correlation to the Hammett parameter of the substituent and measuredcarbon nanotube FET response. Nano Letters 3(10):1421–1423

15. Kong J, Chapline MG, Dai HJ (2001) Functionalized carbon nanotubes for molecular hydrogensensors. Advanced Materials 13(18):1384–1386

16. Lin Y, Taylor S, Li HP, Fernando KAS, Qu LW, Wang W, Gu LR, Zhou B, Sun YP (2004).Advances toward bioapplications of carbon nanotubes. J Mat Chem 14(4):527–541

17. Tasis D, Tagmatarchis N, Bianco A, Prato M (2006) Chemistry of carbon nanotubes. ChemicalReviews 106(3):1105–1136

18. Kong J, Soh HT, Cassell AM, Quate CF, Dai HJ (1998) Synthesis of individual single-walledcarbon nanotubes on patterned silicon wafers. Nature 395(6705):878–881

19. Sze SM, Ng KK (2006) Tunnel Devices. Physics of Semiconductor Devices. 3rd edn. Wiley,Hoboken p 417

20. Nikolaev P (2004) Gas-phase production of single-walled carbon nanotubes from carbonmonoxide: A review of the HiPCO process. Journal of Nanoscience and Nanotechnology.4(4):307–316

21. Odom TW, Huang JL, Kim P, Lieber CM (1998) Atomic structure and electronic properties ofsingle-walled carbon nanotubes. Nature 391(6662):62–64

22. Aviram A, Ratner MA (1974) Molecular Rectifiers. Chem Phys Lett 29(2):277–28323. Metzger RM (1999) Electrical rectification by a molecule: The advent of unimolecular elec-

tronic devices. Acc Chem Res. 32(11):950–95724. Metzger RM (2003) Unimolecular electrical rectifiers. Chem Rev. 103(9):3803–383425. Metzger RM (2004) Electrical rectification by monolayers of three molecules. Macromolecular

Symposia 212(1):63–7226. Metzger RM (2006) Unimolecular rectifiers: Methods and challenges. Analytica Chimica Acta

568(1–2):146–15527. Chen J, Reed MA, Rawlett AM, Tour JM (1999) Large on-off ratios and negative differential

resistance in a molecular electronic device. Science 286(5444):1550–155228. James DK, Tour JM (2006) Organic synthesis and device testing for molecular electronics.

Aldrichimica Acta 39(2):47–5629. Wang X, Liu F, Andavan GTS, Jing XY, Singh K, Yazdanpanah VR, Bruque N, Pandey RR,

Lake R, Ozkan M, Wang KL, Ozkan CS (2006) Carbon Nanotube-DNA nanoarchitectures andelectronic functionality. Small 2(11):1356–1365

30. Pandey RR, Bruque N, Alam K, Lake RK (2006) Carbon nanotube – molecular resonant tun-neling diode. Physica Status Solidia – Applications and Materials Science 203(2):R5–R7

31. Bruque N, Pandey RR, Lake RK, Wang H, Lewis JP (2005) Electronic transport through aCNT-Pseudopeptide-CNT hybrid material. Molecular Simulation 31(12):859–864

32. Hu H, Bhowmik P, Zhao B, Hamon MA, Itkis ME, Haddon RC (2001) End-group and defectanalysis of soluble single-walled carbon nanotubes. Chem Phys Lett 345(1–2):25–28

33. Thess A, Lee R, Nikolaev P, Dai H, Petit P, Robert J, Xu C, Lee YH, Kim SG, Rinzler AG,Colbert DT, Scuseria GE, Tomanek D, Fischer JE, Smalley RE (1996) Crystalline ropes ofmetallic carbon nanotubes. Science 273(5274):483–487


34. Metzger RM, Panetta CA (1989) Langmuir-blodgett films of potential donor sigma acceptororganic rectifiers. J Mol Elect 5(1):1–17

35. Okazaki N, Sambles JR, Jory MJ, Ashwell GJ (2002) Molecular rectification at 8 K in anAu/C(16)H(33)Q-3CNQ LB film/Au structure. Applied Physics Letters 81(12): 2300–2302

36. Kumar MJ (2007) Molecular Diodes and Applications. Recent Patents on Nanotechnology1:51–57

Hybrid Single Walled Carbon Nanotube FETsfor High Fidelity DNA Detection

Xu Wang, Mihri Ozkan, Gurer Budak, Ziya B. Guvenc, and Cengiz S. Ozkan

Abstract A novel application for detecting specific biomolecules using SWNT-ssDNA nanohybrid is described. SWNT-ssDNA hybrid is formed by conjugatingamino-ended single strand of DNA (ssDNA) with carboxylic group modifiedSWNTs through a straightforward EDC coupling reaction. ssDNA functional-ized SWNT hybrids could be used as high fidelity sensors for biomolecules. Thesensing capability is demonstrated by the change in the electronic properties ofSWNT. Employing DNA functionalized SWNT FETs could lead to dramaticallyincreased sensitivity in biochemical sensing and medical diagnostics applications.

1 Introduction

Carbon nanotubes (CNT) have been utilized widely in nanoelectronic devices suchas field effect transistors (FET) [1], single-electron transistors [2], rectifying diodes[3] and logic circuits [4] due to its unique mechanical, thermal and electrical prop-erties. They are chemically inert and it is difficult to conduct synthetic chemicaltreatment on them because they are resistant to wetting and indissolvable in waterand organic solvents. In order to expand their potential applications in biomedicaland optoelectronic devices, surface functionalization strategies have been exploredby many research groups within recent years. The attachment of chemical functional

X. WangDepartment of Chemical Engineering, University of California, Riverside, CA 92521

M. OzkanDepartment of Electrical Engineering, University of California, Riverside, CA 92521e-mail: [email protected]

G. BudakNanomedicine Research Laboratory, Gazi University, Besevler, Ankara, Turkey 06510

Z.B. GuvencElectronic and Communication Engineering, Cankaya University, Ankara, Turkey 06530e-mail: [email protected]

C.S. Ozkan (�)Department of Mechanical Engineering, University of California, Riverside, CA 92521e-mail: [email protected]

D. Baleanu et al. (eds.), New Trends in Nanotechnology and FractionalCalculus Applications, DOI 10.1007/978-90-481-3293-5 2,c� Springer Science+Business Media B.V. 2010

17

[email protected]

[email protected]

[email protected]

18 X. Wang et al.

groups represents a strategy for overcoming the disadvantages of CNTs and hasbecome attractive for synthetic chemists and materials scientists. Functionaliza-tion can improve CNTs solubility and processibility, and will allow combinationof unique properties of CNTs with those of other types of materials. The function-alization of CNTs can be divided into covalent and noncovalent types. Covalentfunctionalization is based on covalent linkage of functional entities onto CNTs endsand/or sidewall. Non-covalent functionalization is mainly based on the adsorptionforces between functional entities and CNTs, such as van der waals and -stackinginteraction. With the successful surface functionalization of CNTs, various strate-gies of forming CNT hybrids with chemicals, polymers, and biological species havebeen developed, including fluorination of nanotubes [5], cholorination of nanotubes[6], formation of carbon nanotube-acyl amides [7], and carbon nanotube-esters [8].The integration of biomaterials, such as proteins, enzymes, antigens, antibodies, andnucleic acids with CNTs would combine the conductive or semiconductive proper-ties of CNTs with recognition or catalytic properties of biomaterials. A number ofresearchers focus on DNA assemblies with CNTs because of the molecular recog-nition capability and high aspect ratio nanostructures. DNA has been utilized asscaffolding materials or fabrics with applications in electronics; such constructs in-clude DNA lattices [9], grids [10], tiles [10], ribbons [10], tubes [10], and origami[11] for organizing components of electronics.

CNT-DNA complexes have been assembled via different methods. DNA’s in-teraction with CNT through the physical binding has been explored. DNA’s non-specific binding to CNT wall has been visualized by high resolution transmissionelectron microscopy [12].

DNA transport through a single MWNT cavity has been directly observedby fluorescence microscopy [13]. During the process, both Van der Waals andhydrophobic forces are found to be important, with the former playing a more dom-inant role on CNT-DNA interactions [14]. DNA interaction with CNT throughchemical covalent binding has also been described [15]. The amide linkage isformed by the reaction of carboxylic groups on CNT with the amine groups of ss-DNA in a solution. Such heterostructures indicated a negative differential resistance(NDR) effect indicating a biomimetic route to forming resonant tunneling diodes(RTD). CNT-DNA assemblies have been applied into detection of biomaterials andchemical species. Label free detection of DNA hybridization using carbon nanotubenetwork field-effect transistors [16] has been demonstrated. DNA functionalizedsingle wall carbon nanotubes for electrochemical detection has been reported [17].Most of this prior work presents the sensing capability of CNT networks or CNTfilm structures. In this work, the detection of specific sequences of DNA using asingle SWNT field effect transistor is described. SWNTs are purified and dispersedin o-dichlorobenzene (ortho-dichlorobenzene) solvent before functionalized by ss-DNA. The functionalization is completed by forming an amide linkage betweencarboxylic groups of SWNT and amine groups of ssDNA via the EDC couplingmethod. Modified SWNT based biosensor in the configuration of a field effect tran-sistor (FET) is fabricated using electron beam lithography (EBL). When specificsequences of ssDNA which are complementary to the ssDNA covalently bound on

Hybrid Single Walled Carbon Nanotube FETs for High Fidelity DNA Detection 19

the SWNT surface are exposed to the device, modulation of the current-voltagecharacteristics demonstrate the capability of SWNT-ssDNA nanohybrids for appli-cations in high fidelity biosensing.

2 Experimental Section

2.1 SWNT Purification and Dispersion

SWNTs with carboxylic functional groups in 2.73 wt% were purchased from CheapTubes, Inc. They were first purified and dispersed following a previously definedprocedure [18] as follows: SWNT-COOH (1 mg) was added in o-dichlorobenzene(o-DCB) solvent (10 mL), followed by sonication in an ice bath for 10 min. Soni-cation usually generates a lot of heat, therefore, an ice bath is used for protectingthe SWNTs from physical damage. After sonication, the mixture solution was cen-trifuged for 90 min at 13,000 rpm. The supernatant was then further centrifuged at55,000 rpm for 2 h. The resulting supernatant solution is almost transparent, and theresulting functionalized SWNTs are shown in Fig. 1.

a b

c d

Fig. 1 SWNT purification and dispersion process. (a) SEM image of commercial carboxylic groupfunctionalized SWNTs. (b) SWNTs sonicated in ODCB for 5 min. (c) Supernatant of SWNT so-lution collected after centrifugation at 13,000 rpm for 90 min. (d) Supernatant of SWNT solutioncollected after centrifugation at 55,000 rpm for 2 h

20 X. Wang et al.

2.2 Device Fabrication

A drop of purified SWNT dispersion solution was deposited on a marked heavilydoped pCSi=SiO2 (300 nm) substrate. After the solution was dried at room temper-ature, discrete SWNTs and groups were left on the surface of the substrate. Metalelectrode contacts were deposited at the ends of a single SWNT by using elec-tron beam lithography and lift-off patterning (Fig. 2). Initial electrical testing wascarried out by sweeping the back-gate voltage from �10 to C10V under a fixedsource-drain voltage at 1 V using an Agilent 4155C semiconductor parametric ana-lyzer. Current–voltage (I–V ) measurements indicated that the SWNT was of p-type(Fig. 3).

Fig. 2 (a) SEM image of SWNT field effect transistor fabricated with electron beam lithography.(b) AFM image of another SWNT FET device

Fig. 3 I–Vg measurementsof the SWNT FET forVds D 1V with a gate oxidethickness of 500 nm

−10 −8 −6 −4 −2 0 2 4 6 8 10

1.5

2.0

2.5

3.0

Cur

rent

(uA

)

Voltage (v)

Hybrid Single Walled Carbon Nanotube FETs for High Fidelity DNA Detection 21

2.3 Synthesis of SWNT-ssDNA Conjugations and Detectionof Specific DNA Sequences

SWNT-ssDNA conjugations were formed by reacting the amine group at the endof a single strand DNA with the carboxylic group on the surface of SWNTs viathe EDC coupling reagent. Since SWNTs were fixed by the metal electrodes onthe substrate, the substrate was immersed into the EDC solution for 30 minutes.Amine functional group modified ssDNA (sequence: 50-CTCTCTCTC-NH2�30,from Sigma-Gynosis) and NHS-sulfo reagent were added to the solution. After in-cubating for 12 h, the sample was dried at room temperature. During the incubationprocess, ssDNA molecules bound to the SWNT surfaces via amide linkage. Afterobtaining an initial I–V measurement of the SWNT-ssDNA FET structure, it wasthen immersed into a complementary strand DNA (cDNA) solution where fragmentswith the complementary sequence of 50-GAGAGAGAG-30 were hybridized to thessDNA at 42 C for 4 h. I–V measurements were conducted and the modulation ofthe conductivity was recorded.

3 Results and Discussion

Commercial SWNTs were dispersed in dionized water, and a drop of dispersionsolution was dried on a silicon substrate and imaged as reference (Fig. 1a). A lotof impurities, such as carbonaceous graphite particles, sonopolymers that wereinvolved during SWNT fabrication and acid oxidization are observed. Most ofSWNTs bundle together due to van der waals interactions between SWNTs. Af-ter sonication in o-DCB, a drop of sample was taken for SEM imaging (Fig. 1b),indicating the dispersion of SWNTs becoming much better although impurities stillexisted. According to our experience, o-DCB exhibits stronger �-orbital interactionwith the sidewalls of SWNTs. During a sonication process, o-DCB molecules pen-etrate SWNT bundles by overcoming the van der waals interaction [18]. Therefore,sonication of SWNTs in o-DCB is critical to obtain well dispersed SWNTs. In orderto remove the impurities, centrifuging with different speeds conducted. Centrifug-ing under low speed was performed first, followed by ultra-centrifugation under highspeed. Larger impurities settled down and were excluded after the first centrifuga-tion step (Fig. 1c). With the centrifugation speed increasing, a decreasing number ofSWNTs with an increase in quality (much less impurities) as shown in Fig. 1d.

Purified SWNTs were deposited on a pC doped silicon substrate capped with500 nm SiO2. SWNT field effect transistors were fabricated via electron beamlithography. Figure 2a shows the configuration of the device. A single SWNT wasfixed at both ends by metal electrode contacts patterned by electron beam evapora-tion. The contacts made in this way are reliable for a long time and can withstandimmersion in water bath [19]. Another sample is presented by AFM imaging inFig. 2b. Most of SWNTs after dispersion have a diameter of 15–20 nm, and are

22 X. Wang et al.

isolated from each other in a well dispersed manner. SWNT FET characterizationwas carried out by measuring the current between source and drain electrodes undergate voltage sweeping. I–V curve in Fig. 3 shows that the current is decreasing withapplying a positive voltage, which demonstrates that the SWNT in the FET is of ap-type semiconductor.

Due to the carboxylic groups of SWNT, amino ended ssDNA readily binds toSWNT under EDC coupling and NHS-sulfo reagents acting in the solution. AfterssDNA attach to the carboxylic group sites on the surface of SWNT, the functional-ized SWNT was immersed into a target DNA (cDNA) solution. SWNT serves as thesemiconductor, and ssDNA bound along the surface of SWNT serves as the recep-tors for the target DNA fragments. I–V measurements of SWNT, SWNT-ssDNAhybrids and SWNT-ssDNA-cDNA hybrids were recorded respectively. From theI–V curves (Fig. 4), after ssDNA fragments covalently bind to the SWNT, the con-ductivity of the SWNT is reduced (Fig. 4, red) compared to that of before binding(Fig. 4, black). We suggest that upon SWNT-ssDNA binding, geometric deforma-tions occurs, leading to charge carrier scattering sites in the SWNT, hence thereduced conductivity [20]. With the target DNA hybridizing with ssDNA, the con-ductivity increases (Fig. 4, green). The increase in conductivity is due to an increasein the density of negative charges at the SWNT surface associated with the bindingof cDNA. In the sensor device, ssDNA serves not only as receptors for targets, butalso as the gate dielectric. When cDNA is added, ssDNA hybridizes with cDNA in-stead of binding to SWNT directly. cDNA molecules bear negative charges on theirbackbone. Even though cDNA is dried during the measurements, residual watermolecules from the buffer solution are still adsorbed on DNA’s hydrophilic phos-phoric acid backbone by forming hydrogen bonds [21], together with the cationscounterbalancing the negative charge of DNA [22]. Also, the effect of measurementenvironment after DNA molecules dryed could not be ignored [23, 24]. Under ahigh humidity level, water molecules would accumulate at the phosphate backboneof DNA [24]. The electrical measurements in this paper are conducted under an am-bient humidity level of 40%. Therefore, cDNA molecules bear negative charges with

Fig. 4 I–V curves of SWNTbefore and after ssDNAcovalent binding (black andred). I–V measurements ofssDNA-SWNT nanohybridsdetecting the target DNA(cDNA) is shown in green

−5 −4 −3 −2 −1 0 1 2 3 4 5−8

−6

−4

−2

0

2

4

6

Cur

rent

(uA

)

Voltage (V)

SWNT

SWNT-ssDNA

SWNT-ssDNA-cDNA

New Trends in Nanotechnology and Fractional Calculus ...download.e-bookshelf.de/download/0000/0728/79/L-G-0000072879... · Çankaya University, Balgat-Ankara, Turkey ... scientists

Documents